Hitherto, there have been proposed various electric bicycles of the type having a manually operated driving power and a motor operated driving power arranged in parallel such that the former driving power is assisted by means of an electric motor within a predetermined range which varies according to the pedal load. In such an electric bicycle, it is necessary to control the range of assistance by a motor powered driving assembly in such a manner that such assistance be 50% of bicycle speed in the case of a bicycle speed of from 0 to 15 km/h and, within a bicycle speed range of from 15 km/h to 24 km/h, it be gradually decreased according to the bicycle speed, the assistance being reduced to 0% when a bicycle speed of 24 km/h is reached.
Therefore, the motor powered driving assembly includes a pedal load sensor for detecting a pedal load, a pedal speed sensor for detecting the rotational speed of the pedal, an electric motor, a speed reduction mechanism, and a control circuit. The control circuit controls the electric motor on the basis of information from both the pedal load sensor and pedal speed sensor so as to provide for power assistance within the predetermined range.
In addition, the electric bicycle has a rechargeable battery for use as an electric energy source.
Specifically, one such prior art arrangement is disclosed in Japanese Patent Application Laid-Open No. 7-40878. In this prior art arrangement, a motor powered driving assembly is set up integrally with the bicycle at a location adjacent main pipe and seat pipe members of the body frame. In fact, however, it has been difficult to arrange that all components of the assembly, including an electric motor, a speed reduction mechanism, a control circuit, a pedal load sensor, and a pedal speed sensor, are integrally mounted together beneath a pedal crank shaft.
Further, components such as electric motor, speed reduction mechanism, control circuit, pedal load sensor, and pedal speed sensor are arranged in spaced apart relation, and this requires wiring for electrically interconnecting these components. Therefore, for protection of the wiring it is necessary to cover the entire assembly of such components with a resin cover.
Whilst, from the standpoints of ease of riding and ease of handling, the position of gravity center of the bicycle is important. In this connection, it must be considered that the weight of the rider is considerably heavier than the weight of the bicycle, so that the center of gravity during bicycle riding is positioned considerably higher than the gravity center of the bicycle itself. Therefore, it is required that the position of gravity center of the bicycle itself be set as much low as possible and centrally between the front and rear wheels.
However, with prior art electric bicycles, it is inevitable that the center of gravity of the bicycle is positioned rather high since the motor powered driving assembly is mounted in an inner space defined by bicycle frame members or above the pedal crank shaft. As such, the prior art electric bicycles have been unsatisfactory from the view points of ease of riding and ease of handling.